Anorexia Nervosa (AN) is a serious psychiatric disorder with substantial morbidity and a lifetime mortality arguably as high as that associated with any psychiatric illness. A major contributor to the poor prognosis of this illness is the high rate of relapse which follows successful initial treatment. Patients with AN often exhibit symptoms of other psychiatric disorders, such a major depression and obsessive compulsive disorder, which respond favourably to treatment with medication. It is surprising therefore that medication treatment for AN has been consistently unsuccessful. Virtually all of the controlled trials of medication have been conducted during the initial phase of treatment, when patients are underweight. It is possible that medications are of limited utility during that phase of illness because of physiological and neurochemical effects of starvation. Therefore, it may be useful to explore the utility of medication among patients with AN after initial treatment has reversed the acute effects of starvation. The goal of the current proposal is to determine whether the SSRI fluoxetine, compared to placebo, reduces the rate of relapse and enhances psychological and behavioural recovery following initial treatment for AN. In order to answer this question, a two-site (New York and Toronto), four-year collaborative R01 study is proposed. Eighty patients with AN who have successfully completed initial treatment in an inpatient or intensive outpatient program will be randomly assigned to receive fluoxetine or placebo for 12 months under double-blind conditions while receiving appropriate psychological treatment. Outcome will be assessed on the basis of maintenance of weight and reduction in psychopathological symptoms characteristic of AN.